It has been established that rapidly labeled heterogeneous nuclear RNA in eukaryotic cells is complexed with protein almost immediately upon synthesis. Recent work from our laboratory has demonstrated that some RNA in nuclear ribonucleoprotein (nRNP) is readily accessible to exogenous nuclease while other regions, sharing certain sequence characteristics, are well protected. We now wish to extend this work to globin nuclear RNA in dimethylsulfoxide induced Friend erythroleukemia cells. Probes specific for globin nuclear RNA, and various portions of that sequence, will be prepared by restriction endonuclease digestion of the cloned mouse beta-globin major gene. These will be used to map the portions of nuclear globin RNA (including the inserts) which are accessible to, or protected from, exogenous nuclease. This work will define the globin nRNP structure in precise terms which will permit us to investigate specific questions regarding the components of the structure and its role in RNA modification, processing, and transport.